1. Field of the Invention
The present invention relates to a three-dimensional plastic sheet that can be produced in great quantities by means of offset printing, and more particularly, to a three-dimensional plastic sheet that has an array of identical semispherical convex lenses formed on the top surface thereof, such that a three-dimensional image can be vividly seen even at every positions irrespective of the position or direction of the plastic sheet, while greatly minimizing the generation of moire patterns caused by the interference of different color dots.
2. Background of the Related Art
Generally, a three-dimensional plastic sheet is formed of a lenticular screen that has an array of semi-cylindrical lenses each having a pitch of about 0.5 mm formed on the top surface of the sheet. In case of a three-dimensional photographic printing, the images of an object seen by left and right eyes are each printed on a sheet of lenticular screen, thereby obtaining a three-dimensional image where the object looks like floating in the space or going away into the space when seen through the two eyes.
In this case, the lenticular screen that has the plurality of semi-cylindrical lenses serially arranged on the top surface of the plastic sheet gives the three-dimensional effect just to the left and right sides with respect to the length direction of each lens, but does not give any three-dimensional effect to the upper and lower sides thereof, such that there is a defect in that the viewing angle for the three-dimensional image is limited.
On the other hand, a conventional three-dimensional plastic sheet is formed in such a fashion that a printed surface seen through a lens layer having an array of lenses formed thereon is recognized thus to observe a designed three-dimensional image, wherein the printed surface is processed by means of general offset printing, for production in great quantities. At this time, there occurs a problem that since the conventional plastic sheet does not have any high resolution due to the embossing effect of the lenses seen through the lens layer, the printed screen cannot be vivid and clear.
On a general offset printing screen, moreover, numerous dots constituting the printed screen are refracted on the lens layer to cause the generation of moire patterns or dizzy illusion due to the interference of the dots, such that more vivid three-dimensional screen cannot be provided.
With the conventional three-dimensional plastic sheet processed by means of the offset printing, therefore, a simple pattern of three-dimensional image should be displayed through one-color printing, which makes it difficult to display a three-dimensional effect through four-primary color printing or special effects (for example, two-way transformation, motion, and morph effects) in a lenticular technique.
In some cases, of course, there has been presented a three-dimensional method using IP (integral photography) technique as introduced by M. G. Lippmann in France, 1908, which is not practical in use because of requiring a high precision of machining technique and a high resolution of photography technique.